Controller for fluid operated device

ABSTRACT

A controller for a fluid pressure operated device has a section for metering control fluid through the controller to the pressure operated device. The meter section of the controller is enclosed in a pressurizable housing. A static pressure head equal to the control fluid pressure within the meter is applied to the casing and acts on the external surfaces of the meter to eliminate leakage out of metering elements during operation of the controller and to thereby reduce or eliminate &#39;&#39;&#39;&#39;slip&#39;&#39;&#39;&#39; between an input member of the controller and the fluid pressure operated device. Additionally, this pressure head is used to create a frictional braking force resisting movement of the movable element of the meter.

United States Patent [191 Larson Apr. 2, 1974 [54] CONTROLLER FOR FLUID OPERATED 2,962,973 12/1960 Pettibone 418/133 X DEVICE [75] lnventorz. Bernard J. Larson, New Hope, pmrmry Cmyle MinnL Assistant ExammerMichael Koczo, Jr.

' Attorney, Agent, or FirmTeagno 8!. Toddy [73] Assignee: Eaton Corporation, Cleveland, Ohio [22] Filed: Apr. 3, 1972 [57] ABSTRACT [21 L N 24 ,41 A controller for a fluid pressure operated device has a section for metering control fluid through the controller to the pressure operated device. The meter section [52] 418/61 60/384 180/792 R of the controller is enclosed in a pressurizable hous- [51] Int. Cl B62d 5/06, F15b 9/00 A Static pressure head equal to the control fluid [58] Field 0156811211 418/130, 131, 133, 61; pressure within the meter is pp to the Casing and ISO/79.2 R; 91/467, 375, 388; 60/384 acts on the external surfaces of the meter to eliminate leakage 'out of metering elements during operation of [56] References C'ted the controller and to thereby reduce or eliminate UNITED STATES PATENTS slip between an input member of the controller and 3,385,057 5/1968 Pruvot et al. 418/61 x the fl i pressure Operated device- Additionally, this 3,452,543 7/1969 Goff et al 418/61 X pressure head is used to create a frictional braking 3, /197 Whi e 418/181 X force resisting movement of the movable element of 3,404,634 10/1968 Connelly 418/133 h t 3,240,158 3/1966 'Brundage..,. 418/133 2,984,215 2/1962 Charlson 91/467 6 Claims, Drawing Figures PATENTEDAPR 2mm 3.801.239

sum 2 [If 2 FIG4 CONTROLLER FOR FLUID OPERATED DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to controllers for fluid pressure operated devices such as hydrostatic steering systems, where a mechanical input signal is converted to a mechanical output signal solely by the metering of pressurized hydraulic fluid without a mechanical interconnection between the input and the output. More specifically, this invention relates to a controller of the above general type having means for preventing slip between input and output and for creating a travel limit stop.

2. Discussion of the Prior Art Controllers of the aformentioned general type are known in the art. One such prior art controller is disclosed and claimed in U.S. Pat. RE. 25,126, issued Feb. 20, 1942 to Charlson and now assigned to the assignee of the present invention. However, one problem of prior art devices has been that because of leakage within the meter of the controller, a positive position reference between the input and-the output could not be maintained. For example, in the case where the input is a steering wheel of a vehicle, and the output is a hydraulic cylinder attached to steerable vehicle wheels, then leakage within the meter will result in the steering wheel assuming a different angular position for the straight ahead position of the vehicle wheels each time the system is activated and'then returned to the straight ahead position.

Another problem of this type of device is lack of a positive limit stop on movement of the steering wheel which results in a phenomena which may be called I travel limit slip. In this case, when the cylinder attached to the vehicle wheels reaches the end of its stroke, the steerable vehicle wheels have reached the limit of their travel. However, because of leakage out of the meterof the controller, if the operator continues to apply a turning force to the steering wheel, the steering wheel will continue to turn, although at a slower rate. The rate of steering wheel rotation at this position is known as travel limit slip rate and is measured in revolutions per minute of the steering wheel.

Furthermore, as the vehicles on which these devices are used get larger, higher pressures are required in order to enable the operator to effectively steer the vehicle. However, higher pressures increase the rate of leakage and thus further aggravate the aforementioned problems.

It is to these problems of leakage in the meter section and provision of a travel limit stop in a controller for fluid pressure operated devices that the present invention is directed.

Others have attempted to control leakage in fluid pumps or motors, however, to date no one has successfully eliminated leakage of the meter section of a controller for fluid pressure operated devices.

Some prior art patents relating to control of leakage in fluid pumps or motors are US. Pat. Nos: 211,582, issued Jan. 21, 1879 to Nash; 2,434,135, issued Jan. 6, 1948 to Witchger; 3,240,158, issued Mar. 15, 1966 to Brundage; 3,246,835, issued Apr. 19, 1966 to Linder; and 3,551,079, issued Dec. 29, 1970 to Brundage.

In the preferred form of the present invention, the controller is generally of the type shown in U. S. Reissue Pat. No. 25,126 entitled Controller for Fluid Pressure Operated Devices, issued Feb. 20, 1962 to Lynn L. Charlson and assigned to the assignee of the present invention. As previously stated, one of the major problems of prior art devices was the problem of travel limit slip rate. Travel limit slip rate may be defined as the rate in RPMs at which the steering wheel of a totally hydraulic steering system will continue to rotate after the mechanical portions of the steered wheels have reached the limits of travel. This phenomenon occurs primarily because of the failure of a totally hydraulic steering system to provide a direct mechanical connection between the steering wheel and the steered wheels of the vehicle. Thus, in a totally hydraulic steering system leakage between the surfaces of the metering device results in a slip or movement of the steering wheel for which there is no corresponding movement of the steering vehicle wheels. This problem is most clearly emphasized by the fact that in a totally hydraulic steering system using prior art controllers, the steering wheel and steered wheels of the vehicle do not continuously remain in the same phase relationship. In other words, after making a sharp turn, the vehicle operator may find that, when he redirects the vehicle down a straight line path, the position of his steering wheel has moved relative to the straight ahead position as a result of slip within the controller.-

Since it is usually undesirable and many times impossible to provide a direct mechanical connection between the fluid controller and the steered vehicle wheels, up to the present time this problem has remained unsolved. However, since hydraulic fluid is substantially incompressible, if leakage losses across the metering portions of a fluid controller can be substantially reduced or eliminated, then s1ip" can be reduced or eliminated. Also, if a frictional braking force acting on the movable element of the controller at the limit of steering travel can be provided, a travel limit stop exists and travel limit slip" can be eliminated.

The primary purposes for this invention are to reduce leakage in the meter section of a controller, to provide a travel limit stop in controllers for fluid pressure operated devices and to extend the operating pressures for such controllers. In order to make it possible for the meter section of a controllerto withstand high pressures without deformation and excessive leakage, the meter section of the controller is enclosed in a pressurizable housing. With the meter thus enclosed, the external surfaces of the metering section can be subjected to full system pressure by allowing pressure from one of the pockets of the meter displacement element to communicate with the interior chamber of the housing.

This external pressurization of the meter section provides at least four advantages in a controller of the type disclosed in the aforementioned Pat. RE 25,126.

1. By internal and external pressure equalization of the metering section, the stationary outer element of the meter remains geometrically unchanged irrespective of the operating pressure. This promotes smoother action of the meter element and more precise metering of fluid since the inner rotatable element relies on the outer stationary element to maintain its orbiting circular motion and precise metering function.

2. As pressures increase, the tensional load on the members holding the meter section together increases proportionally. By external pressurization of the end of the meter, the tensional loading on these members and the meter element increasing the end clearance at these interfaces. This allows meter oil to leak away at an increased rate.

With external pressure on the end cap and the end cap thickness designed to promote a controlled deflection, it is possible to inwardly deflect the end cap towards the movable element to minimize end clearance's. This inward deflection is caused by the force imbalance due to a differential in areas presented to pressure on either side of the end cap. It should be noted that the center of the movable element of the meter RE 25,l26 is subjected only to low return line pressure of the system.

4. The increase of fluid pressure due to bottoming of the steering cylinder, may be used to provide a frictional braking force resisting further movement of the meter element to provide a travel limit stop.

Accordingly, it is an object of the present invention to provide a controller for a fluid operated device wherein an increase of fluid pressure due to the fluid operated mechanical device reaching the limit of its movement may be used to create a frictional braking force resisting further movement of a metering element of the controller to thereby provide a travel limit stop.

Another object of the present invention is to provide a fluid controller having a metering portion for meter-' ing control fluid to the fluid operated device and wherein the cotroller has means for both radially and axially pressure biasing the metering elements into engagement and wherein the biasing pressure is substantially equal to or greater than the control fluid pressure and acts through differential pressure areas to create a biasing force for accomplishing the above-stated pur pose.

Another object of the present invention is to provide a fluid controller of the type disclosed and claimed in U.S. Pat. RE 25,126 having a pressurizable housing surrounding and enclosing a metering portion of the fluid controller whereby leakage losses may be reduced or eliminated across the metering portion of the controller.

Another object of the present invention is to provide an improved controller for fluid pressure operated devices wherein the controller has a metering section which measures the volume of fluid flow to the fluid operat ed device and including means operable to apply fluid pressure to the metering section of the controller to prevent leakage between movable and stationary meter surfaces and thereby insure a more precise metering control fluid passing to the fluid pressure operated device.

Another object of the present invention is to provide a controller for fluid pressure operated devices wherein the controller has a metering means for measuring the volume of control fluid and wherein hydraulic fluid pressure within the metering means is balanced by hydraulic fluid pressure outside of the metering means to thereby prevent distortion of the metering means and insure more accurate metering of the control fluid.

- Another object of the present invention is to provide a fluid controller having a meter and wherein fluid pressure is applied to one end surface of the meter to prevent leakage across the other end surface thereof.

Other objects and advantages of the present invention will become apparent from the following detailed specification, claims and drawings which follow hereinafter.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation of the controller of the present invention disposed in a hydraulic circuit.

6-4; at FIG. 2. Y

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is preferably used in hydrostatic steering system to provide a better position reference between a steering wheel of the vehicle and the steered wheels of the vehicle to thereby eliminate travel limit slip and provide a travel limit stop in a hydraulic steering system without the necessity of a mechanical interconnection between the steering wheel and the steered vehicle wheels.

In the preferred embodiment of the invention the controller is indicated in its entirety by the numeral 10 and, for the purpose of the present'example, is illustrated in FIG. 1 as used in a power steering mechanism of the vehicle (not shown). The controller 10 has a housing or body structure 12 having an inlet 13 to which is connected a conduit 14 to which fluid under pressure is introduced to the controller 10 from a suitable source, such as a pump 15 that is connected to a reservoir or tank 16 by conduit 17. The casing 12 is further provided with an outlet 18 for return of fluid to the tank or reservoir 16 through a conduit 19 suitably connected to the outlet 18. The casing 12 has a pair of ports 20 and 21 to which the respective conduits 22 and 23 are connected, these conduits lead to opposite ends of a hydraulic cylinder 24 having mounted for axial reciprocatory movement therein a piston equipped plunger rod 25. The plunger rod 25 is adapted to be connected to a steering link 26 of the vehicle (not shown), by means of the usual bell crank 27 and rigid link 28. The steering linkage 26 is connected to the steerable wheels 29 in the usual manner. The housing or body structure 12 comprises a tubular section 30 for defining the inlet and outlet 13 and 18 respectively and the ports 20 and 21. A pressure relief valve 31 is provided between conduits l4 and 19. The relief valve setting is approximately three times as high as normal system working pressure of the controller 10.

With reference to FIG. 2 the controller further includes a hearing or end seal plate 32, an internally toothed member 34 and an end cap or seal plate 36. The plate 32, internally toothed member 34, and end cap 36 are secured in end to end relationship to the one end of the tubular section 30 by means of machine screws 38.

The tubular housing section 30 has an internal cylinderical wall 40 which, defines a chamber in which are disposed concentric primary and follow up valve elements 41 and 42 respectively. The follow up valve element 42 is in the nature of the tubular sleeve which closely engages the inner cylinderical wall 40 for rotary movement about an axis of the housing. The cylindrical wall 40 is provided with a plurality of annular grooves 40a, 40b, 40c and 40d each of which is connected to one of the ports 18, 21, 22 and 13 respectively. One of the axial ends of the valve element 42 abuttingly engages plate 32 to prevent axial movement of valve element 42.

The primary valve element 41 is cylindrical in form and hollow for the greater part of its length, to thereby define a recess or passage 48 which extends inwardly from the end thereof adjacent the end plate 32. As can be seen in FIG. 2, bore 48 is open to annular groove 40a associated with outlet port 18 and is thus always exposed to return or low pressure. The valve 41 is nestingly received within the follow up valve element 42 and is concentric therewith. One end of the primary valve element 41 is in substantially abutting relationship with the plate 32, the opposite end of the valve element abuttingly engages a trust bearing 44 mounted in the housing 30 and is supported by an end retainer 45. The primary valve element 41 has a splined recess 50 at one end thereof. A control shaft 52 (see FIG. .1) is rotatably supported relative to the housing 12 and is connected for positive driving rotation to primary valve element by engagement with the splined recess 50. The other end portion of the control shaft 50 is splined or otherwise arranged for reception thereon of a suitable control elements such as a steerng wheel 54 or the like as shown in FIG. 1.

The primary valve element 41 is coupled to the follow up valve element 42 for limited rotary movement in opposite direction with respect to the follow up element 42, and for common rotary movement with the follow up valve element 42. Means for thus coupling the valve elements together comprises a transverse drive pin 56 which extends radially through a pair of diameterically opposed circumferentially extending slots 58 (see FIG. 5) in the primary valve element 41. The opposite ends of the drive pin 56 are snugly received in diameterically opposed aperatures 60 in the follow up valve element 42. When the primary valve element 41 is rotated in either direction of its neutral position, the drive pin 56 becomes engaged by the opposite ends of the opposed slots 58 after which continued rotary movement of the primary valve element 41 will cause similar rotary movement to be imparted to the follow up element 42. For the purpose of yieldingly urging the valve elements 41 and 42 toward neutral relationship wherein the drive pin 56 is centered in the slots 58, a plurality of resilient leaf springs 62 (see FIG. 6) which extend radially through aligned opposed notches 64 and 66 in the primary and follow up valve elements 41 and 42 respectively are provided. A series of grooves and flow passages 41a and 42a are provided in elements 41 and 42 to enable the elements 41 and 42 to control flow of fluid through the controller. These are better shown in aforementioned U.S. Pat. RE 25,126.

The internally toothed member 34 comprises the stator of a meter which measures control fluid to the fluid pressure operated device. The rotor of the meter comprises an externally toothed member 70 having a less number of teeth 72 than the internally toothed member 34. The externally toothed member 70 is adapted to rotate on its own axis and partake of orbital movement about an axis of the member 34. The members 34 and 70 are so arranged that the teeth thereof move into and out of intermeshing engagement and define expanding and contracting fluid chambers 74 during rotary and orbital movement of the member 70. Drive shaft means are provided to drivingly connect follow up valve element 42 for rotation in synchronism with the externally toothed member 70. This driving connection is accomplished by means of a splined bore 76 in member 70 which drivingly engages a splined end 82 of member 80 and pin 56 which is drivingly engaged by a slot 84 in the other end of drive member 80. Drive member 80 passes through the end wall 32 by a clearance bore 32a therein. This clearance is necessary in order to allow end 82 of shaft 80 to partake of orbital movement with member 70. A cylindrical spacer block 77 is provided to fill most of the remaining axial distance of splined bore 76. The splined teeth of bore 76 are thus open to bore 48 and are thus likewise always exposed to the return or low pressure at groove 40a. The construction and operation of the fluid controller up to this point is more clearly set forth in U. S. Pat. Re. 25,126 issued Feb. 20, 1962 to L. L. Charlson and assigned to the assignee of the present invention. Since the description of the structure and operation of the fluid controller up to this point is essentially identical to the device disclosed in the U.S. Pat. Re. 25,126 further description is believed unnecessary to understanding of the invention. The specification of that patent is hereby incorporated by reference into the specification of the present invention.

For the present, it is sufficient to note that upon movement of the steering wheel 54, primary valve element 41 is rotated causing pressurized fluid to flow from the inlet 13 through the expanding and contracting chambers 74 to one of the ports 20 or 21 to move the piston rod 25. The other port 20 or 21 is simultaneously connected to outlet 18 and tank I6. Pressurized fluid in the chambers 74 causes rotational and orbital movement of externally toothed member 70 which in turn rotates follow up valve element 42 to close off the flow. Movement of the member 70 thus meters the volume of fluid fed to the cylinder 24. The reader is referred to the specification of Reissued patent 25,l26 for more detailed understanding of the portions of the fluid controller previously described.

It should be noted that a separate portion of the housing 12 from that portion which houses the valve elements 41, 42, is provided to house the metering elements of the fluid controller. One advantage of this type of structure in the present invention is that subsequent pressurization of the external surfaces of the metering mechanism will have no effect on the valve mechanism.

As previously stated, the metering section of the fluid controller 10 comprises a first end plate 32, a stationary internally toothed member 34, rotatable and orbital externally toothed member 70 disposed therein and a second plate member 36. The plate members 32 and 36 are placed over the ends of the internally and externally toothed members 34 and 70 respectively and sealingly engage the end surfaces of internally toothed member 34. A slight clearance,- less than 0.001 inches, exists between the ends of externally toothed member 70 and plates 32 and 36. The fluid metering means thus is defined by a pair of axially spaced end walls 90 and 92 respectively, one of which is normally disposed in sealing engagement with each end of the internally toothed member 34 and adjacent surfaces of externally toothed member 70. Thus a slight clearance or fluid flow path may initially exist between each end of member 70 and the adjacent end walls. In order to provide a biasing force acting on the metering section which is proportional to pressure within the metering section of the fluid controller, a heavy walled pressurizable casing 100 is provided which is operable upon pressurization thereof to create both radial and axial biasing forces which balance the radial and axialpressures within the metering section to thereby eliminate distortion of the metering section due to pressure therewithin and thereby eliminate or reduce leakage between the respective portions of the metering section. A retaining ring 102 engaging a groove 104 of the housing 12 and a'seal 106 are provided to maintain the casing 100 in engagement with the housing 12 and to prevent leakage therefrom. At assembly, the retaining ring 102 is inserted through a slot 107 in the casing 100 and fed along the groove 104 until it reaches the other end of slot 107. 7

As shown in FIG. 2, one end of the splined bore 76 in the externally toothed member 70 is sealed by a plate 108 across the end thereof to prevent pressurized hydraulic fluid from leaking from the expanding and contracting chambers 74 into the splined bore 76 which as previously stated is normally at outlet pressure. Alternatively the splined bore 76 could be made a blind recess to accomplish the same result.

Pressure on the end surface of member 70 adjacent end wall 92 will thus create a greater axial force acting on member 70 than the force created by pressure adjacent end wall 90. This is because a larger effective area is exposed to high pressure in the displacement chambers 74.

The end plate 36 is further provided with a passage or orifice 110 extending through the center thereof and communicating between the end surface of the externally toothed member 70 and the interior of the pressurizable casing 100.

DESCRIPTION OF OPERATION When the operator turns the steering wheel 54, pressurized fluid flows from the pump 15 through inlet 13, through primary and follow up valve elements 40 and 41 to the chambers 74. Upon initial pressurization of chambers 74, plate member 36 will deform slightly to increase the a fluid flow path from the expanding and contracting chambers 74 along end wall 92 and through passage 110 to the interior of pressurizable housing 100. As pressure in the housing 100 increases, end wall.92 on plate member 36 will return to the undeformed position adjacent the end surface of the externally toothed member. Further, the pressure acting on the end surface of externally toothed member 70 adjacent wall 92 will bias the externally toothed member 70 into frictional sealing engagement with the surface 90 of plate member 32. thereby closing off any clearance between member 70 and end wall 90 and increasing the clearance or flow path between member 70 and end wall 92. Frictional sealing engagement between the sur-' face 90 and the abutting end of externally toothed member 70, causes a relatively slight frictional force resisting rotation of member 70.

However, the only resistance to rotation of the steering wheel that the operator can detect at this time is the resistance of springs 62 to relative rotation of the valve members 41, 42. This is because pressurized fluid is acting within the chambers 74 to drive member 80 and follow up valve element 42 to close off the flow. In other words, in order to rotate the member 70, the pressurized fluid must overcome all frictional forces within the controller as well as the steering load at the wheels 29. Thus, until relief valve pressure is reached in the system, the operator can only sense the resistance of springs 62 to rotation of the steering wheel. The pump 15 will supply what ever pressure is needed to cause movement of member 70 up to the relief valve pressure.

When piston 25 bottoms in cylinder 24, further attempts to rotate the steering wheel 54 will still deform springs 62 causing relative movement of primary and follow up valve members 41 and 42. This allows the pump to supply more fluid to the system. However, since piston 24 is at the limit of its travel, the fluid becomes trapped and system pressure increases instantaneously to relief valve pressure. This increases the nor mal component of the frictional force at surface 90 by several times since this normal force is proportional to system pressure.

Since a frictional force is equal to a friction coefiicient times the normal force, the frictional force at surface 90 likewise increases proportionately.

Bottoming of the piston 25 in cylinder 24 thus causes an effective braking action on member at the travel limit of the steering system is provided. Since the bore 76 of externally toothed member adjacent the drive shaft 80 is normally exposed to low or return pressure, the pressure on member 70 at end wall 92 thus prevents flow from the high pressure within the expandingand contracting fluid chambers 74 to the low pressure at bore 76 and end wall 90. Thus, leakage losses along this surface are substantially eliminated. As working pressure increases, the sealing force increases. With this construction, a slight clearance between the end of externally toothed member 70 and the sealing surface 92 of plate member 36 will occur. However, this is not entirely objectionable because this is a metering device.

Pressures within each of the expanding and contracting fluid chambers 74 are substantially equal. Since pressure in the chambers is substantially equal, little or no flow or leakage will occur along surface 92 between the chambers. Plate member 18 seals the bore 76 and prevents leakage to the bore 76 at surface 92.

The hydraulic imbalance necessary to reduce the clearance between the externally toothed member 70 of the meter and the surface and provide the aforementioned braking action is created by the difference in end areas of the externally toothed member 70 exposed to pressure. This pressure imbalance results in a predictable axial force being applied to the externally toothed member 70 to cause frictional and sealing engagement with end plate 32 at surface 90. The axial force is defined by the pressure times the area of the splined hole 76 in the center of the externally toothed member 70 of the meter. This force or thrust load creates a certain frictional drag at this interface 90 which results in reducing the travel limit slip rate to near at any system pressure above approximately 500 PSI. This frictional drag is not noticable to the operator except at either end of the steering cylinder stroke. The hydraulic pressure differential across the meter element to overcome this frictional drag is inversely proportional to meter element displacement per revolution.

Pressurization of the casing 100 further acts radially upon the external surface of the internally toothed member 34 to prevent radial deformation thereof which further increases the efficiency of this device as a fluid memter by decreasing fluid leakage losses.

This version of the high pressure controller design does not require controlled deflection of the end cap 36. Oil is admitted under pressure through a center hole 110 in the end cap 36 to pressurize casing 100. It is felt the pressure admitted into the casing at this point will have less fluctuation with respect to variations of pressure within the meter element.

In a modified form of the preferred embodiment as shown in FIG. 4, sealing of the bore in the externally toothed member may be eliminated by providing a different fluid flow path for pressurization of the casing 100. As shown in FIG. 4, like elements previously designated with respect toFIG. 2 are shown in FIG. 4 by the same numeral with a prime attached. As previously stated, in the embodiment of FIG. 4, the bore 76' of the externally toothed member 70 may be left open and the plate 108 eliminated. This is because pressurized fluid flow for pressurization of casing 100' is accomplished by an alternate method. Internally toothed member 34 is provided with a notch or groove I communicating between one of the expanding or contracting fluid chambers and the interior of casing 100'. In this modified version, the plate member 36 must be designed to be controllably deflected by working pres sure within the controller. By this method, since the bore 76 of externally toothed member 70' is left open and exposed to low pressure, a differential force acts on plate member 36. This differential force controllably deflects plate 36' inwardly to urge both the externally and internally toothed member into substantial sealing engagement with the surfaces 90 and 92' thereby eliminatingor reducing leakages. The radial pressure within the casing 100' would likewise act on the external peripheral surface of internally toothed member 34 to eliminate distortion of externally toothed member 34 caused by pressurization of the chambers 74'.

Since plate 36 is designed to be deflected slightly by working pressure within the system, it will be deflected to a much greater extent when cylinder 24 bottoms at the travel limit and back pressure on the plate 36 increases to relief valve pressure. This is because relief valve pressure is usually several times normal working pressure.

This increased deflection of plate 36' will act on externally toothed members 70' to cause frictional engagement at the surfaces 90 and 92' thereby acting as a brake on externally toothed member 70 and providing an effective travel limit stop. Frictional engagement between the externally toothed member 74 and surfaces 90 and 92' and elimination of leakage from the chambers 74' therefore acts to eliminate slip and provide a substantially positive travel limit stop.

A further advantage of either of the aforementioned embodiments is that if the hydraulic pump 15 should fail, resulting in a loss of control fluid pressure, the frictional braking force acting on member at surfaces and 92' will also be released. The importance of this is that when pump failure occurs, the operator must exert enough force on the steering wheel to'cause the metering portion to pump fluid for steering the vehicle. Thus, elimination of the added friction at surfaces 90 or 90 and 92 makes iteasier for the operator to control the vehicle during such an emergency.

I claim:

1. A controller for a fluid pressure operated device, said controller comprising a housing having an inlet port, and a control fluid outlet port, a member disposed in said housing and movable under the influence of fluid pressure to meter the volume of fluid which passes out of said control port during operation of said controller, and means for applying a braking force to said movable member which is proportional to the outlet pressure at said control port,

said movable member comprising an externally toothed member having parallel end surfaces, said housing including an internally toothed member, and parallel end walls, said externally toothed member being disposed between said end walls with its opposite end surfaces adjacent thereto, the teeth of said members intermeshing .to form expanding and contracting fluid chambers for metering control fluid during operation of said controller,

said means for applying a braking force to said movable member comprising means for pressure bias-' ing one of the ends of said externally toothed member into frictional engagement with one of said end walls including said movable member having a bore extending axially therethrough, said bore normally being exposed to a pressure which is substantially below the pressure in said fluid chambers, means for sealing said bore to prevent flow therethrough, and a leakage clearance between one of said end surfaces and the adjacent end wall whereby one of said end surfaces may be exposed to pressure in said fluid chambers.

2. The invention of claim 1 including a pressurizable casing surrounding and enclosing said internally and externally toothed members, and means for pressurizing said casing to the pressure in said fluid chambers to thereby control distortion of said members due to fluid pressure in said chambers during operation of said controller.

3. The invention of claim 2 wherein said means for pressurizing said casing includes passage means extending from said leakage clearance through one of said end walls to the interior of said casing.

4. A controller for a fluid operated device, said controller comprising a housing, a first portion of said housing having an internally toothed member and a pair of axially spaced fixed end walls defining a chamber,

an externally toothed member disposed for orbital and rotational movement about an axis in the chamber, the teeth of said internally and externally toothed members forming expanding and contracting volume chambers during relative movement therebetween to measure the volume of fluid which passes through said chamber, said externally toothed member having parallel end surfaces and a splined bore extending axially therethrough,

a second portion of said housing defining an inlet port, a return port, a control port, and a valve chamber,

valve means disposed in the valve chamber and operable to feed an exhaust pressurized fluid through said expanding and contracting volume chambers upon movement thereof, and

drive means connecting said valve means for follow up movement in synchronism with one of the movements of said externally toothed member, said drive means including a shaft having a splined end received in and drivingly engaging the splined bore of said externally toothed member,

the improvement which comprises said externally toothed member having a counterbored recess in one end surface thereof surrounding said splined bore, a plate member disposed in said recess and sealing said splined bore to prevent fluid leakage therethrough and to provide a continuous end surface extending across one end of said externally toothed member, the distance between said fixed end walls of said housing being slightly greater than the width of said externally toothed member to enable one of the end surfaces of said externally toothed member to be entirely exposed to fluid pressure in the expanding and contracting volume chambers, and means in said housing for directly exposing at least a portion of the other end surface of said externally toothed member to a relatively lower fluid pressure to provide a resultant axial force acting on said externally toothed member andurging said externally toothed member into y 12 sealing engagement with one of said end walls.

5. The invention of claim 4 including a pressurizable casing surrounding and enclosing said internally and externally toothed members, and means for pressurizing said casing to the pressure in said fluid chambers during operation of said controller to thereby control distortion of said members due to fluid pressure in said chambers.

6. A controller for a fluid pressure operated device, said controller, comprising a housing, a firstportion of said housing having an internally toothed member and a pair of axially spaced end walls defining a pressurizable metering chamber,

an externally toothed member disposed in said chamber for rotational and orbital movement about an axis thereof, the teeth of said members interengaging to form expanding and contracting volume chambers during relative movement therebetween,

said externally toothed member having an end surface disposed parallel to and in confronting relationship with each of said end walls,

means for exposing one of the end surfaces of said externally toothed member directly to the fluid pressure in said expanding and contracting volume chambers, and means for exposing at least a portion of the opposite end surface of said externally toothed member directly to a lower fluid pressure to provide a resultant axial force acting directly on said one end surface of said externally toothed member urging said externally toothed member into sealing engagement with the opposite end wall of said metering chamber during operation of said controller.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,801,239 Dated Agril 2, 197A lnv n fl Bernard J. Larson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 56: "ootroller" should read --controller---u Column 8, line 58: "18" should read ---lO8---.

Column 9, line 17: "memter" should read ---meter---.

3 Signed and sealed this 16th day of July 197a.

Q (SEAL) Attest:

McCOY' M. GIBSON, JR. C.. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-IOSO (1069) UQCOMM'DC 60376-3 69 US. GOVERNMENT PRINTING OFFICE: I969 0-368-33l, 

1. A controller for a fluid pressure operated device, said controller comprising a housing having an inlet port, and a control fluid outlet port, a member disposed in said housing and movable under the influence of fluid pressure to meter the volume of fluid which passes out of said control port during operation of said controller, and means for applying a braking force to said movable member which is proportional to the outlet pressure at said control port, said movable member comprising an externally toothed member having parallel end surfaces, said housing including an internally toothed member, and parallel end walls, said externally toothed member being disposed between said end walls with its opposite end surfaces adjacent thereto, the teeth of said members intermeshing to form expanding and contracting fluid chambers for metering control fluid during operation of said controller, said means for applying a braking force to said movable member comprising means for pressure biasing one of the ends of said externally toothed member into frictional engagement with one of said end walls including said movable member having a bore extending axially therethrough, said bore normally being exposed to a pressure which is substantially below the pressure in said fluid chambers, means for sealing said bore to prevent flow therethrough, and a leakage clearance between one of said end surfaces and the adjacent end wall whereby one of said end surfaces may be exposed to pressure in said fluid chambers.
 2. The invention of claim 1 including a pressurizable casing surrounding and enclosing said internally and externally toothed members, and means for pressurizing said casing to the pressure in said fluid chambers to thereby control distortion of said members due to fluid pressure in said chambers during operation of said controller.
 3. The invention of claim 2 wherein said means for pressurizing said casing includes passage means extending from said leakage clearance through one of said end walls to the interior of said casing.
 4. A controller for a fluid operated device, said controller comprising a housing, a first portion of said housing having an internally toothed member and a pair of axially spaced fixed end walls defining a chamber, an externally toothed member disposed for orbital and rotational movement about an axis in the chamber, the teeth of said internally and externally toothed members forming expanding and contracting volume chambers during relative movement therebetween to measure the volume of fluid which passes through said chamber, said externally toothed member having parallel end surfaces and a splined bore extending axially therethrough, a second portion of said housing defining an inlet port, a return port, a control port, and a valve chamber, valve means disposed in the valve chamber and operable to feed an exhaust pressurized fluid through said expanding and contracting volume chambers upon movement thereof, and drive means connecting said valve means for follow up movement in synchronism with one of the movements of said externally toothed member, said drive means including a shaft having a splined end received in and drivingly engaging the splined bore of said externally toothed member, the improvement which comprises said externally toothed member having a counterbored recess in one end surface thereof surrounding said splined bore, a plate member disposed in said recess and sealing said splined bore to prevent fluid leakage therethrough and to provide a continuous end surface extending across one end of said externally toothed member, the distance between said fixed end walls of said housing being slightly greater than the width of said externally toothed member to enable one of the end surfaces of said externally toothed member to be entirely exposed to fluid pressure in the expanding and contracting volume chambers, and means in said housing for directly exposing at least a portion of the other end surface of said externally toothed member to a relatively lower fluid pressure to provide a resultant axial force acting on said externally toothed member and urging said externally toothed member into sealing engagement with one of said end walls.
 5. The invention of claim 4 including a pressurizable casing surrounding and enclosing said internally and externally toothed members, and means for pressurizing said casing to the pressure in said fluid chambers during operation of said controller to thereby control distortion of said members due to fluid pressure in said chambers.
 6. A controller for a fluid pressure operated device, said controller comprising a housing, a first portion of said housing having an internally toothed member and a pair of axially spaced end walls defining a pressurizable metering chamber, an externally toothed member disposed in said chamber for rotational and orbital movement about an axis thereof, the teeth of said members interengaging to form expanding and contracting volume chambers during relative movement therebetween, said externally toothed member having an end surface disposed parallel to and in confronting relationship with each of said end walls, means for exposing one of the end surfaces of said externally toothed member directly to the fluid pressure in said expanding and contracting volume chambers, and means for exposing at least a portion of the opposite end surface of said externally toothed member directly to a lower fluid pressure to provide a resultant axial force acting directly on said one end surface of said externally toothed member urging said externally toothed member into sealing engagement with the opposite end wall of said metering chamber during operation of said controller. 